1) Technical Field
The present invention relates generally to the field of polymeric foam production, and more particularly to polymeric foams made from the combination of two subcombinations generally referred to as an "A" portion and a "B" portion, wherein the B portion includes a polyol and the A portion contains an isocyanate.
2) Background Information
Various foamed materials may be produced using polymeric materials derived from a wide variety of materials and mixtures of materials, including polyolefins, styrenes, polyurethanes, and virtually any other base material originally in the solid state which cures to form a solid and substantially elastic mass having air pockets, cavities, or voids located throughout its bulk which were induced by the expansion of a gas within the bulk during the change of the material from the liquid to the solid state, this phase change being commonly referred to as the "curing" of the base material.
In the prior art, various methods have been devised using a wide range of materials for producing foamed materials from polymeric materials. Within the general class of foamed materials are included those familiar to those skilled in the art as polyurethanes and polyisocyanurates. Generally speaking, these materials are formed by a combination of two subcombinations of materials, commonly referred to by those of ordinary skill in the art as an "A" portion and a "B" portion.
Typically, the B portion of a subcombination from which a polyurethane may be formed contains a polyol component containing a plurality of hydroxyl groups in each molecule which are capable of reacting with the isocyanate groups present in a selected organic isocyanate (contained in the A portion) when the A and B portions are combined to form a polyurethane. The B portion typically contains ingredients additional to the polyol such as catalysts for promoting the reaction between the polyol and isocyanate; surfactants which enhance the interactions of the finished product with a substrate to which it is to be applied and assist in promoting homogeneity between the various components in the A portion; fire retardants; adhesion promoters; pigments; etc. It is generally preferred that the various components of the B portion are blended together to form a homogeneous mixture to which the A part of the formulation may be subsequently added. Under such an arrangement, the B portion may be made up en masse and stored for later admixture with the A portion at a desired time.
The A portion of the formulation typically consists only of the isocyanate used. When the B portion is combined with the A portion, a reaction between the polyol with the isocyanate occurs, and a polyurethane is formed. An isocyanurate is formed when an isocyanate molecule reacts with other isocyanate molecules to form a ring structure comprising three isocyanate molecules. A common scenario known to occur by those skilled in this art is where the polyol and isocyanate molecules react first with one another to form a polyurethane, with the liberation of heat. The heat thus liberated in situ is absorbed by other molecules within the reaction mixture, and especially other molecules of isocyanates. Isocyanate molecules which have absorbed sufficient thermal energy may then go on to react with one another to form polyisocyanurates within the polyurethane. Catalysts which promote the formation of polyisocyanurates are known to those skilled in this art, and generally comprise potassium salts of carboxylic acids having fewer than 12 carbon atoms per molecule, and quaternary ammonium salts.
Typically, a blowing agent is mixed in with at least one of either the A and B portions before or immediately after the mixing of the A and B portions with one another, under conditions sufficient to ensure that the blowing agent is capable of expanding during the curing process (either by the application of heat from the surroundings, or by liberation of heat from a chemical reaction occurring as a result of the curing of the polymeric material, or as a result of subjecting the whole mixture to a pressure change) so as to cause gaseous pockets to form within the whole mass of curable material during its cure, to produce a finished foam material. The curable material may be either a thermoset or thermoplastic.
The type and number of chemical materials useful as blowing agents in the prior art is large, and many may be used successfully according to the teachings herein. Suitable candidate materials for use as blowing agents include those capable of rapidly undergoing expansion, and which are inert with respect to the other components of the curable mixture. Historically, conventional blowing agents have been selected from the groups of compounds including hydrocarbons, halogenated hydrocarbons (including without limitation chlorinated hydrocarbons and chlorofluorocarbons), nitrogen, and carbon dioxide. However, in view of recent proclamations by various National and Regional governments, governmental agencies and non-governmental organizations, the use of halogenated materials, and especially halogenated hydrocarbons, as blowing agents has met great disfavor. Accordingly, the most preferable blowing agents for producing foamed materials are hydrocarbons, with two of the most preferable blowing agents being cyclopentane and isopentane. However, these blowing agents are not soluble in the polyol sub-portion of the polyurethane formulation, and hence must be incorporated into the final product using high degrees of mechanical mixing to form emulsions which are generally not stable and which tend to produce gas pockets in finished foam products having a broad polydispersity with respect to their size dimension. To date, attempts at producing single-phase mixtures containing polyols for polyurethane production which contain blowing agent as soluble components have met only limited success. An example of one such attempt is contained in the teachings of U.S. Pat. No. 5,578,652, the entire contents of which are incorporated by reference thereto. The dicyclopentadiene used therein is an especially hazardous material to work with.